Updates inventory information for a Product while respecting the last update timestamps of each inventory field. This process is asynchronous and does not require the Product to exist before updating fulfillment information. If the request is valid, the update is enqueued and processed downstream. As a consequence, when a response is returned, updates are not immediately manifested in the Product queried by ProductService.GetProduct or ProductService.ListProducts. When inventory is updated with ProductService.CreateProduct and ProductService.UpdateProduct, the specified inventory field value(s) overwrite any existing value(s) while ignoring the last update time for this field. Furthermore, the last update times for the specified inventory fields are overwritten by the times of the ProductService.CreateProduct or ProductService.UpdateProduct request. If no inventory fields are set in CreateProductRequest.product, then any pre-existing inventory information for this product is used. If no inventory fields are set in SetInventoryRequest.set_mask, then any existing inventory information is preserved. Pre-existing inventory information can only be updated with ProductService.SetInventory, ProductService.AddFulfillmentPlaces, and ProductService.RemoveFulfillmentPlaces. The returned Operations is obsolete after one day, and the GetOperation API returns NOT_FOUND afterwards. If conflicting updates are issued, the Operations associated with the stale updates are not marked as done until they are obsolete.